Techniques for suppressing multiple resonance modes in a quasi-statically operated movable mirror

ABSTRACT

A projector includes a mirror quasi-statically driven by a drive signal to scan a laser beam in a pattern. A drive circuit generates the drive signal so the mirror moves in a non-linear fashion, yielding unwanted resonances. The non-linearity results in movement of the mirror through a first projection area, into a dead zone, and into a second projection area. The laser beam is emitted as the mirror moves through the first and second projection areas, but not the dead zone. A controller samples a feedback signal of the mirror as it moves through the first and second projection areas, producing first and second projection area sample which are processed to produce first and second ripple measurements. First and second correction signals are generated as a function of the ripple measurements. The drive circuit applies the correction signals to the drive signal so that the unwanted resonances are attenuated.

TECHNICAL FIELD

This disclosure relates generally to image projection, and, moreparticularly, to techniques for use by laser scanning projectors (usedfor image projection) to suppress multiple unwanted resonance modes thatarise in quasi-statically operated movable mirrors when thosequasi-statically operated movable mirrors are driven in a non-linearfashion, or when such mirrors are driven in a linear mode.

BACKGROUND

Laser scanning projectors constructed from microelectromechanical system(MEMS) components can be relatively small, and therefore implementedinto easily portable devices such as picoprojectors. These laserscanning projectors can be used to display fixed or moving video imageson a screen, wall, lens (in the case of a smartglass wearable), oruser's skin (in the case of a smartwatch wearable). Since modern digitalmedia is often in a high definition format, it is desirable for suchlaser scanning projectors to be capable of image display in highdefinition.

In general, MEMS laser scanning projectors function by opticallycombining red, green, and blue laser beams to form an RGB laser beam,and then directing the RGB laser beam to either a bi-axial mirror, or aset of two uni-axial mirrors working in tandem, with one of the axesbeing a fast axis and the other axis being a slow axis. Driving of slowaxis movement of the mirror (whether it be a bi-axial mirror or auni-axial mirror) is performed quasi-statically and linearly, typicallyat a low frequency of around 60 Hz.

This linear slow-axis movement drives the mirror from its minimal angleto its maximal angle in two phases. In a “trace” phase, the mirror isdriven slowly from its minimal angle to its maximal angle linearly,while the RGB laser beam is directed so as to impinge upon the mirror.In a “retrace mode”, the mirror is driven quickly back from its maximalangle to its minimal angle linearly, while the RGB laser is modulated sothat it is not impinging upon the mirror.

Shown via the lines of 8 of FIG. 1A is a graph of a driving signal forthe mirror vs. time, when quasi-statically and linearly driven. As canbe observed, in the trace phase 10A, the drive signal rises from aminimal amount to a maximal amount of 1 in 15 milliseconds, and in theretrace phase 10B, the signal drops from the maximal amount to zero inunder two milliseconds. A second cycle is shown, with the trace phase11A and retrace phase 11B.

In some cases, non-linear drive may be desired during the trace mode.With a non-linear drive during the trace mode, shown as the line 9 inFIG. 1A, the trace phase 10A is separated into three zones, namely afirst projection zone 1A during which the RGB laser is directed so as toimpinge upon the mirror, a dead zone 2A during which the RGB laser ismodulated so that it is not impinging upon the mirror, and a secondprojection zone 3A during which the RGB laser is directed so as toimpinge upon the mirror. Since the RGB laser is not to impinge upon themirror in the dead zone 2A, movement of the mirror can be sped up duringthe dead zone as 2A compared to movement during the first and secondprojection zones 1A, 3A.

The fast transitions between the first projection zone and dead zone,and between the dead zone and second projection mode, introduce unwantedresonance into the mirror movement. This is shown in FIG. 1B, where theactual movement 15 of the mirror itself when driven by the non-lineardrive signal 9 is shown compared to the non-linear drive signal 9. Itcan be observed that the actual movement 15 is comprised of oscillationsor “ripples” that indicate unwanted resonant movement. Movement duringthe retrace phase can also contribute to ripple—in general, any drivemodes of the mirror that are not smooth cause ripple.

Note that ripples are similarly present in the actual movement 12 of themirror when driven by the linear drive signal 8. Prior art ripplesuppression techniques are capable of attenuating the ripples presentwhen the linear drive signal 8 is used, however, these prior art ripplesuppression techniques do not function when the non-linear drive signal9 is used.

Therefore, further development is required.

SUMMARY

Described herein is a laser scanning projector. The laser scanningprojector may include a collimated light source that emits a beam ofcollimated light, and a movable mirror driven by a drive signal so thatwhen the beam of collimated light impinges upon the movable mirror it isscanned in a scan pattern. A drive circuit generates the drive signalsuch that as the movable mirror moves in the scan pattern, unwantedresonance movement of the movable mirror occurs. A controller receives afeedback signal from the movable mirror, samples the feedback signalwhile the movable mirror moves in the scan pattern, processes a firstset of samples to produce a first ripple measurement, processes a secondset of samples to produce a second ripple measurement, generates firstand second correction signals as a function of the first and secondripple measurements, and causes the drive circuit to apply the first andsecond correction signals to the drive signal so that the unwantedresonance movement of the movable mirror, generated due to movement ofthe movable mirror in the scan pattern, is attenuated.

In some cases, the controller may process the first and second sets ofsamples to produce the ripple measurement by estimating a first trendfunction from the first set of samples, and estimating a second trendfunction from the second set of samples, subtracting the first trendfunction from the first set of samples to produce first de-trendedsamples, and subtracting the second trend function from the second setof samples to produce second de-trended samples, and performing adiscrete fourier transform of the first de-trended samples and of thesecond de-trended samples.

The controller may process the first and second sets of samples toproduce the ripple measurement by selecting a first frequency bin,resulting from the discrete fourier transform which performed on thefirst de-trended samples, which corresponds to a first frequency ofunwanted resonance movement of the movable mirror, selecting a secondfrequency bin, resulting from the discrete fourier transform whichperformed on the second de-trended samples, which corresponds to asecond frequency of unwanted resonance movement of the movable mirror,and generating a scalar error function from the first and secondfrequency bins.

The controller may generate the first and second correction signals suchthat the first and second correction signals serve to minimize thescalar error function. The controller may determine the first and secondcorrection signals that minimize the scalar error function using aquasi-Newton method.

The first and second frequencies of unwanted resonance movement may bethe same.

The movable mirror may be a microelectromechanical (MEMS) mirror.

The movable mirror may be driven by the drive circuit in a linearfashion.

The movable mirror may be driven by the drive circuit in a quasi-staticfashion.

The movable mirror may be driven by the drive circuit in anelectrostatic fashion.

The movable mirror may be driven by the drive circuit in a magneticfashion.

The movable mirror may be driven by the drive circuit in a piezoelectricfashion.

The unwanted resonance movement may include multiple resonances atdifference frequencies.

The unwanted resonance movement may be a single resonance at a singlefrequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graph of drive signals for a movable mirror in both alinear drive mode and a non-linear drive mode.

FIG. 1B is a graph of drive signals for a movable mirror vs. actualmovement of the movable mirror in both a linear drive mode and anon-linear drive mode.

FIG. 2A is a block diagram of a laser scanning projector on which thecontrol techniques and methods described herein may be performed.

FIG. 2B is a block diagram of another configuration of laser scanningprojector on which the control techniques and methods described hereinmay be performed.

FIG. 3 is a further block diagram of the laser scanning projector ofFIG. 2A in which the mirror control circuitry is shown.

FIG. 4 is a graph showing the non-linear drive signal of FIG. 3 duringthe trace phase.

FIG. 5 shows a feedback signal from the slow axis mirror of FIG. 3, assampled by the analog to digital converter.

FIG. 6A shows the ripples in the samples of the first projection sectionand a determined trend line for those samples.

FIG. 6B shows samples of the first projection section after trendreduction.

FIG. 6C shows results of a discrete Fourier transform performed on thede-trended samples of FIG. 6B.

FIG. 7 shows the non-linear drive signal of FIG. 3, and locations on thenon-linear drive signal where the correction control signal is applied.

DETAILED DESCRIPTION

One or more embodiments of the present disclosure will be describedbelow. These described embodiments are only examples of the presentlydisclosed techniques. Additionally, in an effort to provide a concisedescription, all features of an actual implementation may not bedescribed in the specification.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

Described herein with initial reference to FIG. 2A is a laser scanningprojector 100, such as may be used in a self-contained pico-projector ora pico-projector unit incorporated within a portable device such as asmartphone. The laser scanning projector 100 includes a red laser 102,green laser 104, and blue laser 106. These lasers 102, 104, 106 operateto generate beams of collimated light 103, 105, 107 which are combinedby a beam combiner 108 into an RGB laser or RGB beam of collimated light109.

A mirror apparatus 110 receives the RGB laser 109 and reflects it onto atarget 120. In greater detail, the mirror apparatus 110 includes a fastaxis mirror 112 receiving the RGB laser 109 and reflecting it toward aslow axis mirror 114, which in turn reflects it onto the target 120. Thefast axis mirror 112 is controlled to scan the RGB laser 109 between settravel limits for the fast axis, and the slow axis mirror 114 iscontrolled to scan the RGB laser 109 between set travel limits for theslow axis. The fast axis is typically a horizontal axis while the slowaxis is typically the vertical axis, although in some cases the conversemay be true.

The fast axis mirror 112 may be a resonating mirror, while the slow axismirror 114 may be a quasi-static mirror. The slow axis mirror 114 may bedisplaced using magnetic, electro static, or piezoelectric forces. Thefast axis mirror likewise may be displaced using magnetic, electrostatic, or piezoelectric forces. In some cases, instead of a separatefast axis mirror 112 and a separate slow axis mirror 114, a singlebiaxial mirror may be used that is driven on both a fast axis and a slowaxis.

In some instances, such as shown in FIG. 2B the laser scanning projector100 includes a single laser 199, such as an infrared laser, that emits alaser beam 198 toward a mirror 197, which in turn reflects the laserbeam 198 onto the target 120. The mirror 197 is biaxial, and thus isdriven on both a fast axis and a slow axis. In other cases, the mirror197 may instead use a mirror apparatus 110 with both a fast axis mirror112 and slow axis mirror 114, such as shown in FIG. 2A.

As shown in FIG. 3 viewed in conjunction with FIG. 2A, the laserscanning projector 100 includes mirror drive circuitry 130, whichgenerates a drive signal 133 for the slow axis mirror 114. This drivesignal 133 is a non-linear drive signal (which will be described ingreater detail below) that drives the slow axis mirror 114quasi-statically. An analog to digital converter (ADC) 117 receives afeedback signal 123 generated by the slow axis mirror 114, and digitizesthe feedback signal 123 so as to produce a digital feedback signal 113.

Mirror control circuitry 116 receives the digital feedback signal 113,processes the digital feedback signal 113 (as will be described below),and generates control signal 131 for the mirror drive circuitry 130based upon that processing. The mirror control may be a microprocessor,an application specific integrated circuit (ASIC), or other suitableprogrammable device.

The mirror drive circuitry 130 generates the drive signal 133 as afunction of the control signal 131. As stated, the drive signal 133 isnon-linear, specifically during the trace mode. As shown in FIG. 4, thetrace mode is separated into three zones: a first projection zone 1during which the RGB laser 109 is modulated as to impinge upon the slowaxis mirror 114, a dead zone 2 during which the RGB laser 109 ismodulated so that it is not impinging upon the slow axis mirror 114(e.g. is not present), and a second projection zone 3 during which theRGB laser 109 is again modulated so as to impinge upon the slow axismirror 114. Since the RGB laser 109 is not to impinge upon the slow axismirror 114 in the dead zone 2, movement of the slow axis mirror 114 canbe sped up during the dead zone as 2 compared to movement during thefirst 1 and second 3 projection zones. This is effectuated by theincrease in slope of the drive signal 133 shown in FIG. 4. Thus inducesripple, as does retrace during the retrace mode. However, it should beunderstood that the below techniques may be used during any drive move,including linear.

While movement during each of the first projection zone 1, dead zone 2,and second projection zone 3 can be considered to be substantiallylinear, the transition between the first projection zone 1 to the deadzone 2, and the transition between the dead zone 2 to the secondprojection zone 3, is not linear. Due to this, as well as due to thenon-linearity of the movement during the entire trace phase (since themovement is quicker during the dead zone 2), the drive signal 133overall is not considered to be linear during the trace mode, althoughit is considered to be linear during the retrace mode.

The fast transitions between the first projection zone and dead zone,and between the dead zone and second projection mode, introduce unwantedresonance into the movement of the slow axis mirror 114. These unwantedresonances can be observed as ripples in the digital feedback signal113, such as those shown in FIG. 5. Here, it can be observed that theamplitude and phase of the ripples occurring in the samples 4 from thefirst projection zone 1 is different than that of the amplitude andwavelength of the ripples occurring in the samples 5 from the secondprojection zone 3, meaning that the ripples observed in the digitalfeedback signal 113 during the first projection zone 1 indicate that adifferent resonance movement is present on the slow axis mirror 114 thanthat indicated by the ripples observed in the digital feedback signal113 during the second projection zone 3. Thus, here, two undesiredresonance movements of the slow axis mirror 114 are indicated by thedigital feedback signal 113. As also shown in FIG. 5, the output issaturated during the dead zone 2, and thus useful data is not containedin samples taken in the dead zone 2.

The processing performed by the mirror control circuitry 116 is togenerate a correction control signal 135 that is used by the mirrordrive circuitry 130 in generating the drive signal 133, the purpose ofwhich is to compensate the driving of the slow axis mirror 114 so thatthe undesired resonance movements (and thus the ripples observed in thedigital feedback signal 113) are attenuated.

This processing will now be described in greater detail. As explained,two sets of samples of the feedback signal 123 are taken by the ADC 117,the first set of samples including the ripples 4 occurring during thefirst projection zone 1, the second set of samples including the ripples5 occurring during the second projection zone 3. For any general case,these sets of samples may be taken at any points, during any projectionzones, during any type of mirror drive, and need not be taken at thespecific points described above. For each of these sets of samples 4 and5, a trend function is estimated by a suitable technique, such aspolynomial regression, potentially a second order polynomial regression.Therefore, first and second trend functions are generated, respectivelycorresponding the first and second sets of samples 4 and 5.

Shown in FIG. 6A is the first trend function A overlaid on the first setof samples 4 for the ripple B is shown in FIG. 6A. Next, the first trendfunction is subtracted from the first set of samples 4 to produce afirst set of de-trended samples C, and the result of this subtraction isshown in FIG. 6B. The second trend function is likewise subtracted fromthe second set of samples 5 to produce a second set of de-trendedsamples.

Next, a discrete Fourier transform is performed on the first and secondsets of de-trended samples, and for each of the sets of de-trendedsamples, a frequency bin corresponding to the associated unwantedresonance frequency is selected. Results of the discrete Fouriertransform for the first set of samples 4 are shown in FIG. 6C.

These frequency bins, labeled R₁ and R₂, can be mathematicallyrepresented as:R ₁ =R _(1_amp) *e ^(iR1_phase)R ₂ =R2_(_amp) *e ^(iR2_phase)Since R1 and R2 are complex values, they can each be represented as twoexpressions. Thus, R1 can be represented as R_(1_real), R_(1_img), andR2 can be represented as R_(2_real), R_(2_img).

A scalar error function f, including both frequency bins, can bemathematically represented as:ƒ(R ₁ ,R ₂)=R _(1_amp) ² +R _(2_amp) ²

If the scalar error function f can be reduced, then the total ripple(and unwanted resonance movements) on the slow axis mirror 114 can bereduced. Thus, ideally, the scalar error function would be minimized.

This minimization, as will be explained in greater detail below, isperformed by determining correction control signals C1 and C2(collectively represented as 135 in FIG. 3) to apply to the mirror drivecircuitry 130 at appropriate times, resulting in a change of the drivesignal 133 that yields a minimized or substantially minimized scalarerror function ƒ. C1 is applied to the mirror drive circuitry 130 duringretrace, while C2 is applied to the mirror drive circuitry 130 duringthe dead zone of the trace. Samples timing of application of C1 and C2to the mirror drive circuitry 130 can be seen in FIG. 7.

C1 and C2 are sinusoidal waveforms, and can be represented as complexnumbers C_(1_real), C_(1_img), C_(2_real), C_(2_img). As C1 and C2 aremodified, during application to the mirror drive circuitry 130, atransition period occurs, and then R₁ and R₂ stabilize into a new ripplescalar error. Since R₁ and R₂ are functions of C1 and C2, C_(1_real),C_(1_img), C_(2_real), and C_(2_img) can be considered as inputs of thescalar error function ƒ. The specific relation between ƒ and C_(1_real),C_(1_img), C_(2_real), C_(2_img) is unknown, and can be represented as:ƒ(C _(1_real) ,C _(1_img) ,C _(2_real) ,C _(2_img))=unknown

Therefore, to minimize ripples and thus unwanted resonance movements,the goal is to find C_(1_real), C_(1_img), C_(2_real), C_(2_img) thatwill minimize ƒ. Mathematically, this can be represented as:[C _(1_real) C _(1_img) C _(2_real) C _(2_img)]=argmin[ƒ(C _(1_real) ,C_(1_img) ,C _(2_real) ,C _(2_img))]

Consequently, the problem to solve mathematically is that of finding aminimum of a multi-dimensional function. This is an optimization problemand can be solved with a variety of techniques. One suitable techniqueis to use a quasi-Newton method, such as theBroyden-Fletcher-Goldfarb-Shanno (BFGS technique). The BFGS technique isknown to those of skill in the art, therefore, for brevity, a detaileddescription will be omitted from this disclosure.

To begin the Broyden-Fletcher-Goldfarb-Shanno technique, in addition toknowing the function ƒ to minimize, the gradient {right arrow over (∇ƒ)}of the function ƒ for C_(k) is to be calculated, with k representing thekth iteration of the loop.

The gradient {right arrow over (∇ƒ)} can be numerically estimated by:

-   -   1. Measuring a current scalar error ƒ(C_(k))=(C_(1_real),        C_(1_img), C_(2_real), C_(2_img)) from the digitized feedback        signal 113.    -   2. Changing one of the corrections in one dimension, {right        arrow over (C)}=[C₁ _(real) S+Δc, C_(1_img), C_(2_real)B,        C_(2_img)]    -   3. Measuring a new current scalar error ƒ({right arrow over        (C)}).    -   4. Calculating a gradient component for this dimension as:

$\frac{\partial f}{\partial C_{1{\_{real}}}} = \frac{{f\left( C_{k} \right)} - {f\left( \overset{\rightharpoonup}{C} \right)}}{\Delta\; c}$

-   -   5. Repeating steps 2-4 for all vector components of C_(k), (a        total number of 4 times in this example) to obtain the gradient        {right arrow over (∇ƒ)} as:

${\Delta\;{f\left( C_{k} \right)}} = \left\lbrack {\frac{\partial f}{\partial C_{1{\_{real}}}}\frac{\partial f}{\partial C_{1{\_{img}}}}\frac{\partial f}{\partial C_{2{\_{img}}}}\frac{\partial f}{\partial C_{2{\_{img}}}}} \right\rbrack$

Now, knowing ƒ and {right arrow over (∇ƒ)}, theBroyden-Fletcher-Goldfarb-Shanno technique can be performed in order todetermine appropriate values for C₁ and C₂ that will minimize ƒ.

Thus, this technique as shown has canceled multiple undesired resonancemovements. Where three or more undesired resonance movements are shown,this technique also functions properly, with additional frequency binsresulting from the discrete Fourier transform and being included in theequations shown above. In addition, this technique may also be appliedto cancel a single undesired resonance movement, and may also be appliedto cancel an undesired resonance or resonances occurring during lineardrive of a mirror. Thus, the above described has been but one use case,and it should be appreciated that this technique is usable to cancel anynumber of undesired resonances in a mirror, regardless of how the mirroris driven.

It should be understood that through this elimination, reduction, and/orattenuation of unwanted resonant movements, the operation andfunctionality of the laser scanning projector itself is improved. Asexplained, prior art ripple suppression systems without sensors thatreport the actual angle of the quasi-statically driven mirror for itsentire range of movement were incapable of dealing with more than oneinduced, unwanted resonance on the quasi-statically driven mirror,rendering the quasi-statically mirror unsuitable and unworkable for itspurpose. However, using the input shaping techniques described herein,more than one induced, unwanted resonance on the quasi-statically drivenmirror can be suppressed, allowing for the proper operation of thequasi-statically driven mirror in instances where the prior artquasi-statically driven mirrors and systems could not be operated. Asstated, this represents a physical improvement of the capabilities ofthe laser scanning projector containing the quasi-statically drivenmirror itself, and an improvement and advance in the technology of thesystem itself, resulting from the techniques described herein. Inaddition to representing an improvement of the capabilities and physicaloperation of the laser scanning projector itself, the steps, blocks, andcalculations described can be thought of as a set of rules that, whenfollowed, enables the laser scanning projector to suppress multipleinduced, unwanted resonances on the quasi-statically driven, which isfunctionality not available in the prior art.

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be envisionedthat do not depart from the scope of the disclosure as disclosed herein.Accordingly, the scope of the disclosure shall be limited only by theattached claims.

The invention claimed is:
 1. A laser scanning projector, comprising: acollimated light source configured to emit a beam of collimated light; amovable mirror driven by a drive signal so that when the beam ofcollimated light impinges upon the movable mirror it is scanned in ascan pattern; a drive circuit configured to generate the drive signalsuch that as the movable mirror moves in the scan pattern, unwantedresonance movement of the movable mirror occurs; a controller configuredto: receive a feedback signal from the movable mirror; sample thefeedback signal while the movable mirror moves in the scan pattern;process a first set of samples to produce a first ripple measurement;process a second set of samples to produce a second ripple measurement;generate first and second correction signals as a function of the firstand second ripple measurements; and cause the drive circuit to apply thefirst and second correction signals to the drive signal so that theunwanted resonance movement of the movable mirror, generated due tomovement of the movable mirror in the scan pattern, is attenuated. 2.The laser scanning projector of claim 1, wherein the controller isconfigured to process the first and second sets of samples to producethe ripple measurement by: estimating a first trend function from thefirst set of samples, and estimating a second trend function from thesecond set of samples; subtracting the first trend function from thefirst set of samples to produce first de-trended samples, andsubtracting the second trend function from the second set of samples toproduce second de-trended samples; and performing a discrete fouriertransform of the first de-trended samples and of the second de-trendedsamples.
 3. The laser scanning projector of claim 2, wherein thecontroller is further configured to process the first and second sets ofsamples to produce the ripple measurement by: selecting a firstfrequency bin, resulting from the discrete fourier transform whichperformed on the first de-trended samples, which corresponds to a firstfrequency of unwanted resonance movement of the movable mirror;selecting a second frequency bin, resulting from the discrete fouriertransform which performed on the second de-trended samples, whichcorresponds to a second frequency of unwanted resonance movement of themovable mirror; and generating a scalar error function from the firstand second frequency bins.
 4. The laser scanning projector of claim 3,wherein the controller is further configured to generate the first andsecond correction signals such that the first and second correctionsignals serve to minimize the scalar error function.
 5. The laserscanning projector of claim 4, wherein the controller is configured todetermine the first and second correction signals that minimize thescalar error function using a quasi-Newton method.
 6. The laser scanningprojector of claim 3, wherein the first and second frequencies ofunwanted resonance movement are the same.
 7. The laser scanningprojector of claim 1, wherein the movable mirror comprises amicroelectromechanical (MEMS) mirror.
 8. The laser scanning projector ofclaim 1, wherein the movable mirror is driven by the drive circuit in alinear fashion.
 9. The laser scanning projector of claim 1, wherein themovable mirror is driven by the drive circuit in a quasi-static fashion.10. The laser scanning projector of claim 1, wherein the movable mirroris driven by the drive circuit in an electrostatic fashion.
 11. Thelaser scanning projector of claim 1, wherein the movable mirror isdriven by the drive circuit in a magnetic fashion.
 12. The laserscanning projector of claim 1, wherein the movable mirror is driven bythe drive circuit in a piezoelectric fashion.
 13. The laser scanningprojector of claim 1, wherein the unwanted resonance movement comprisesmultiple resonances at difference frequencies.
 14. The laser scanningprojector of claim 1, wherein the unwanted resonance movement comprisesa single resonance at a single frequency.
 15. A laser scanningprojector, comprising: a collimated light source configured to emit abeam of collimated light; a movable mirror driven in a quasi-staticfashion by a drive signal so that when the beam of collimated lightimpinges upon the movable mirror it is scanned in a scan pattern; adrive circuit configured to generate the drive signal such that themovable mirror moves from a first angle to a second angle in anon-linear fashion, and moved from the second angle back to the firstangle in a linear fashion, resulting in unwanted resonance movement ofthe movable mirror; wherein generation of the drive signal in thenon-linear fashion results in movement of the movable mirror through afirst projection area, into a dead zone, and then into a secondprojection area; wherein the collimated light source is expected to emitthe beam of collimated light as the movable mirror moves through thefirst projection area and the second projection area, but not as themovable mirror moves through the dead zone; and a controller configuredto: receive a feedback signal from the movable mirror; sample thefeedback signal while the movable mirror moves through the first andsecond projection areas respectively to produce first projection areasamples and second projection area samples; process the first projectionarea samples to produce a first ripple measurement; process the secondprojection area samples to produce a second ripple measurement; generatefirst and second correction signals as a function of the first andsecond ripple measurements; and cause the drive circuit to apply thefirst and second correction signals to the drive signal so that theunwanted resonance movement of the movable mirror, generated due tomovement of the movable mirror in the non-linear fashion, is attenuated.16. The laser scanning projector of claim 15, wherein the controller isconfigured to process the first and second projection area samples toproduce the ripple measurement by: estimating a first trend functionfrom the first projection area samples, and estimating a second trendfunction from the second projection area samples; subtracting the firsttrend function from the first projection area samples to produce firstde-trended projection area samples, and subtracting the second trendfunction from the second projection area samples to produce secondde-trended projection area samples; and performing a discrete fouriertransform of the first de-trended projection area samples and of thesecond de-trended projection area samples.
 17. The laser scanningprojector of claim 16, wherein the controller is further configured toprocess the first and second projection area samples to produce theripple measurement by: selecting a first frequency bin, resulting fromthe discrete fourier transform which performed on the first de-trendedprojection area, which corresponds to a first frequency of unwantedresonance movement of the movable mirror; selecting a second frequencybin, resulting from the discrete fourier transform which performed onthe second de-trended projection area, which corresponds to a secondfrequency of unwanted resonance movement of the movable mirror; andgenerating a scalar error function from the first and second frequencybins.
 18. The laser scanning projector of claim 17, wherein thecontroller is further configured to generate the first and secondcorrection signals such that the first and second correction signalsserve to minimize the scalar error function.
 19. The laser scanningprojector of claim 18, wherein the controller is configured to determinethe first and second correction signals that minimize the scalar errorfunction using a quasi-Newton method.
 20. The laser scanning projectorof claim 18, wherein the controller causes the drive circuit to applythe first correction signal to the movable mirror while it is moved fromthe second projection area back to the first projection area.
 21. Thelaser scanning projector of claim 18, wherein the controller causes thedrive circuit to apply the second correction signal to the movablemirror while it is moved within the dead zone.
 22. The laser scanningprojector of claim 17, wherein the first and second frequencies ofunwanted resonance movement are the same.
 23. The laser scanningprojector of claim 15, wherein the movable mirror comprises amicroelectromechanical (MEMS) mirror.
 24. A laser scanning projector,comprising: a drive circuit configured to generate a drive signal to beused by a movable mirror to be driven in a quasi-static fashion so thatwhen a beam of collimated light impinges upon the movable mirror, it isscanned in a scan pattern; the drive circuit generating the drive signalsuch that the movable mirror moves from a first deflection angle to asecond deflection angle in a non-linear fashion, and moved from thesecond deflection angle back to the first deflection angle in a linearfashion, resulting in unwanted resonance movement of the movable mirror;wherein generation of the drive signal in the non-linear fashion resultsin movement of the movable mirror through a first projection area, intoa dead zone, and then into a second projection area; wherein the beam ofcollimated light is expected to impinge upon the movable mirror as themovable mirror moves through the first projection area and the secondprojection area, but not as the movable mirror moves through the deadzone; and a controller configured to: receive a feedback signalgenerated based upon the movable mirror; sample the feedback signal, atleast partially, while the movable mirror moves through the first andsecond projection areas; process the sampled feedback signal to producea ripple measurement; generate correction signals as a function of theripple measurement; and cause the drive circuit to apply the correctionsignals to the drive signal so that the unwanted resonance movement ofthe movable mirror, generated due to movement of the movable mirror inthe non-linear fashion, is attenuated.
 25. The laser scanning projectorof claim 24, wherein the controller is configured to process the sampledfeedback signals to produce the ripple measurement by: estimating a lowfrequency trend function from the sampled feedback signal; subtractingthe trend function from the sampled feedback signal to produce ade-trended sampled feedback signal; and performing a discrete fouriertransform of the de-trended sampled feedback signal.
 26. The laserscanning projector of claim 25, wherein the controller is furtherconfigured to process the sampled feedback signal by generating a ripplescalar error from the discrete fourier transform; and generating thecorrection signals such that correction signals serve to minimize theripple scalar error.
 27. A method of operating a laser scanningprojector, the method comprising: generating a drive signal that drivesa movable mirror in a quasi-static fashion; wherein the drive signal isgenerated such that the movable mirror moves from a first deflectionangle to a second deflection angle in a non-linear fashion, and movedfrom the second deflection angle back to the first deflection angle in alinear fashion, resulting in unwanted resonance movement of the movablemirror; wherein generation of the drive signal in the non-linear fashionresults in movement of the movable mirror through a first projectionarea, into a dead zone, and then into a second projection area; whereina collimated light source is expected to emit a beam of collimated lightto impinge upon the movable mirror as the movable mirror moves throughthe first projection area and the second projection area, but not as themovable mirror moves through the dead zone; sampling a feedback signalfrom the movable mirror while the movable mirror moves through the firstand second projection areas to produce first projection area samples andsecond projection area samples; processing the first projection areasamples to produce a first ripple measurement; processing the secondprojection area samples to produce a second ripple measurement;generating first and second correction signals as a function of thefirst and second ripple measurements; and applying the first and secondcorrection signals to the movable mirror so that the unwanted resonancemovement of the movable mirror, generated due to movement of the movablemirror in the non-linear fashion, is attenuated.
 28. The method of claim27, wherein the first and second projection area samples are processedto produce the ripple measurement by: estimating a first trend functionfrom the first projection area samples, and estimating a second trendfunction from the second projection area samples; subtracting the firsttrend function from the first projection area samples to produce firstde-trended projection area samples, and subtracting the second trendfunction from the second projection area samples to produce secondde-trended projection area samples; and performing a discrete fouriertransform of the first de-trended projection area samples and of thesecond de-trended projection area samples.
 29. The method of claim 28,wherein the first and second projection area samples are sampled toproduce the ripple measurement by: selecting a first frequency bin,resulting from the discrete fourier transform which performed on thefirst de-trended projection area, which corresponds to a first frequencyof unwanted resonance movement of the movable mirror; selecting a secondfrequency bin, resulting from the discrete fourier transform whichperformed on the second de-trended projection area, which corresponds toa second frequency of unwanted resonance movement of the movable mirror;and generating a scalar error function from the first and secondfrequency bins.
 30. The method of claim 29, wherein the first and secondcorrection signals serve to minimize the scalar error function.
 31. Themethod of claim 30, wherein the first and second correction signals thatminimize the scalar error function are determined using a quasi-Newtonmethod.
 32. The method of claim 29, wherein the first and secondfrequencies of unwanted resonance movement are the same.
 33. The methodof claim 29, wherein the first correction signal is applied to themovable mirror while it is moved from the second projection area back tothe first projection area.
 34. The method of claim 29, wherein thesecond correction signal is applied to the movable mirror while it ismoved within the dead zone.